How to remove rust from steel structure by steel pretreatment line
1、Construction characteristics.
The selection of suitable projectile and projectile gradation ensures the surface roughness of steel after descaling and improves the adhesion of paint film when painting. The method of determining the speed of the conveyor roller compared with the traditional test throwing method ensures the quality of descaling, while saving processing time, improving the efficacy and reducing the cost of descaling. By reasonably adjusting the blast angle and the shutdown of the shot blasting machine, energy consumption can be reduced and the service life of the shot blasting equipment can be extended. Simple operation, advanced technology, reasonable economy and high practicality, with good promotion and application value.
2、Application scope.
Applicable to steel surface cleaning, remove the welded H steel, steel, sections, steel pipe oxidation and rust and steel structure node friction surface treatment construction.
3、Process principle.
Steel shot blasting descaling is the use of shot blasting machine shot blasting machine from different directions of dense shot blasting in the steel surface to remove its oxide, rust and dirt and obtain a certain surface roughness of the descaling method, the process by selecting the appropriate type of shot and different shot gradation to control the surface roughness of the method, different rust levels of the steel surface using different conveyor roller speed to control the projection The method of controlling the blasting time by selecting the right type of shot and different shot grade, the method of controlling the surface roughness by selecting the right type of shot and different shot grade, the method of controlling the blasting time by using different conveying roller speed for different rust grades, the method of controlling the energy consumption by adjusting the blasting angle and shutting down the blasting machine to ensure the descaling grade, improve the descaling quality, increase the production efficiency, save energy and reduce the production cost.
4、Process flow and operation points.
4.1、Process flow.
Selection and grading of shot → control of shot blasting time → adjustment of shot blasting machine's throwing angle according to the structure and height of the workpiece → lifting of the component to the rollerway → starting spraying → lifting of the component away from the rollerway → inspection and acceptance.
4.2, operation points.
4.2.1, the selection and grading of projectile.
(1) The size of the surface roughness of the steel structure before painting has a great impact on the adhesion of the coating, the surface roughness is too small, the paint film lacks the necessary anchorage points, the adhesion is small after complete curing, the coating may occur early damage, peeling, cracking or delamination, etc. If the surface roughness is too large, the amount of paint film is certain to cause uneven distribution of the paint film thickness, especially at the crest of the paint film thickness is lower than the design requirements In addition, bubbles are often trapped in the deeper valleys and will become the root cause of blistering of the paint film, so the surface roughness of the steel after rust removal must be controlled during construction. The type, shape, size and grading of the projectile are important factors affecting the surface roughness after descaling, so the selection and grading of the projectile is developed after repeated tests.
(2) The selection and grading of the shot should make the surface roughness Ry (contour height) of the steel after blasting controlled at 40~60μm, which should be detected by the surface roughness contour meter.
(3) For general construction steel structure with Q235 and Q345 steel, the hardness of the selected shot (Rockwell hardness) is greater than the surface hardness of the member HRC5-25, because when the selected shot is too large, it is easy to break the steel surface and absorb energy and reduce the impact work, and when the selected shot is too small, it is easy to realize the steel surface, absorb energy and reduce the impact work. A moderately hard projectile has good rebound and good rust removal effect. The hardness of the selected projectile (Rockwell hardness) should be controlled at HRC40-50.
(4) The larger the projectile, the better the effect of rust removal, but the greater the surface roughness after rust removal, the smaller the number of projectile grains covered by the same area of the surface of the component, the lower the efficacy, and the adverse effect of excessive roughness on the paint, so the diameter of the projectile should be limited. Choose ￠1, ￠1.4 round cast steel shot and ￠1.2 length 2mm steel cut shot mix.
The steel cut shot is a cylindrical shot formed by cutting steel wire into segments, and the cylindrical angles have a certain scraping effect, which will not damage the surface of the components and can improve the efficiency of rust removal. The ratio of cast steel shot ￠1, ￠1.4 is 2:3, and the ratio of cast steel shot and steel cut shot is 4:6.
4.2.2. Control of shot blasting time.
(1) components placed on the conveyor roller conveyor, with a certain speed slowly convey the components to the blasting chamber, the component end or end of the blasting device is open to the steel shot blasting to the component surface start time to exit the blasting chamber and leave the steel shot blasting surface time for the blasting
The blasting time is the blasting time, and the speed of the conveyor roller is used to control the blasting time in order to achieve the effect of rust removal.
(2) For different rusted steel surfaces, the speed of the conveyor roller conveyor should be smaller for serious rusting and larger for less serious rusting. For the same rust grade steel surface is shot by a certain amount of projectiles to achieve different descaling grades, the speed of the conveyor rollerway with high descaling grade is smaller, and the speed of the conveyor rollerway with low descaling grade is larger. According to the above principle, the speed of conveyor roller conveyor is determined by combining the surface corrosion of the steel being descaled and the descaling grade required by the design.
(3) Determine the rust grade of the steel surface by using the faster-than-sample method, and then determine the appropriate interval speed of the conveyor roller conveyor with the designed descaling grade. Steel surface rust is generally divided into three layers, the outermost layer is Fe2O3 with unstable state, followed by Fe3O4 with stable state, and the innermost state is unstable, so the general descaling of steel structure should beat the FeO layer of innermost FeO. The rust grade of the steel surface is determined by the ratio sample block method. The determination of the grade of rust removal by shot blasting is done by the sample block method, comparing with the sample pictures of national standards.
Determination of steel surface rust grade and descaling grade should be carried out in good diffused daylight or under lighting conditions, and the steel surface to be tested is visually compared with the corresponding photograph. The rust grade shown in the corresponding photo of the more serious rust grade shall be used as the assessment result, and the rust removal grade shall be assessed by the rust removal grade indicated in the photo of the steel surface appearance close to the steel surface.
(4) After the basic interval speed is determined, the speed of the conveyor roller is determined according to the material of the steel, the wear of the pellet or the addition of the pellet, taking a small value for a relatively large surface hardness of the material, a large value for a relatively small surface hardness, a small value for a fresh pellet, and a large value for a serious wear of the pellet.
4.2.3, according to the structure and height of the workpiece, adjust the shot blasting machine shot angle
(1) Because the shot blasting descaling is to throw the projectile to hit the steel surface and achieve the table to observe whether the workpiece run off, timely adjustment; roller conveyor speed control in strict accordance with the requirements of transport.
(2) the machine should be in operation regularly to remove the separator, dust collector in the waste to ensure the normal operation of the equipment. Pay attention to the vibration and sound in the operation of the shot blasting machine is normal, bearing and motor temperature rise, when there is an abnormality in time to stop the inspection, troubleshooting or replacement of the blade.
4.2.6, component lifting open roller conveyor.
After the component is finished removing rust, it will be lifted off the roller road by truss in time, lifted and put to the designated position, and do a good job to protect the finished product.
4.2.7. Inspection and acceptance.
After the rust removal of the components is completed, check the surface roughness and rust removal grade of the components according to the specification requirements, and make inspection and acceptance records.
5、Materials and equipment.
5.1、Materials.
H-beam, steel pipe, steel plate (Q235, Q345), ￠1, ￠1.4 cast steel shot, ￠1.2 length 2mm steel wire shot.
5.2、Machinery equipment.
Roller type shot blasting machine, into the roller truss crane, out of the roller truss crane each 1.
6、Quality control.
(1) Strictly in accordance with the construction quality management system of the processing plant, the establishment and implementation of the quality acceptance system developed by the level of shot blasting descaling, adhere to the three controls of shot gradation, blast angle and speed, in the self-inspection, mutual inspection, process handover inspection on the basis of the principle of acceptance by the quality inspector.
(2) Prepare construction program before construction, and organize training for management and operation personnel participating in the construction, so that each relevant personnel understand construction principles, construction procedures, construction quality control points, know precautions and operating points, and know how to solve problems in the construction process.